Combustion apparatus

ABSTRACT

The combustion apparatus includes a burner configured to generate flame, an ignition section configured to generate spark for igniting the burner, a flame detection section configured to detect the presence or absence of the flame of the burner, and a flame determination section configured to determine, based on a detection result of the flame detection section in a preset determination period, whether or not the flame is generated at the burner. When a predetermined condition is satisfied based on the detection result of the flame detection section in the determination period, the flame determination section determines that the flame is generated. The ignition section generates the spark across a particular period, in which the predetermined condition is not satisfied, of the determination period, and does not generate the spark in the remaining period of the determination period.

BACKGROUND 1. Technical Field

The present invention relates to a combustion apparatus. This application claims priority from Japanese Patent Application No. 2020-142772 filed in Japan on Aug. 26, 2020, the entire contents of which are hereby incorporated by reference.

2. Description of the Related Art

A combustion apparatus includes a flame detection section configured to detect whether or not flame of a burner is generated. The flame detection section detects the presence or absence of the flame of the burner, and combustion of the burner is controlled according to a detection result. As the flame detection section, there is one configured to detect flame by an ultraviolet detector (see, e.g., JP-B-6-100332).

SUMMARY

However, the ultraviolet detector detects, as the flame, not only the flame of the burner but also spark for igniting the burner. For this reason, there is a problem that the ultraviolet detector erroneously detects that the flame is present even though there is no actual flame.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a combustion apparatus capable of preventing erroneous operation due to erroneous detection of spark as flame in a case where a burner generates no flame.

For accomplishing the above-described object, a combustion apparatus according to a certain aspect of the present invention includes a burner configured to generate flame, an ignition section configured to generate spark for igniting the burner, a flame detection section configured to detect the presence or absence of the flame of the burner, and a flame determination section configured to determine, based on a detection result of the flame detection section in a preset determination period, whether or not the flame is generated at the burner. When a predetermined condition is satisfied based on the detection result of the flame detection section in the determination period, the flame determination section determines that the flame is generated. The ignition section generates the spark across a particular period, in which the predetermined condition is not satisfied, of the determination period, and does not generate the spark in the remaining period of the determination period.

According to the above-described configuration, the spark is intermittently generated so that erroneous operation due to erroneous detection of the spark as the flame can be prevented in a case where there is no flame.

Preferably, the flame detection section detects the presence or absence of the flame based on ultraviolet light.

According to the above-described configuration, the presence or absence of the flame can be determined without a direct contact with the flame, and therefore, erroneous operation due to erroneous detection of the spark as the flame can be prevented while the flame detection section with a high durability is used.

Preferably, the particular period is a period in which the burner is ignited without the predetermined condition being satisfied.

According to the above-described configuration, the spark is generated to ignite the burner in the particular period, but determination as the flame being generated is not made because the predetermined condition is not satisfied. Thus, erroneous detection as the flame being present due to the spark can be prevented when there is no flame while the burner is reliably ignited by the spark.

Preferably, the predetermined condition is satisfied according to the number of times of detection as the flame being present by the flame detection section in the determination period.

According to the above-described configuration, an ignition determination level can be easily adjusted according to, e.g., the type of flame detection section and the size of the combustion apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a configuration of a boiler using a combustion apparatus;

FIG. 2 is a time chart showing operation of the combustion apparatus; and

FIG. 3 is a table showing, as results, the number of times of determination as flame being present upon pre-ignition and pilot burner ignition performance (the number of times of successful ignition) when the ratio of ON/OFF time of an igniter is changed.

DESCRIPTION OF THE EMBODIMENTS

A combustion apparatus according to the present disclosure is a combustion apparatus used for, e.g., a boiler. Hereinafter, the combustion apparatus will be described with reference to the drawings. Note that the present invention is not limited to these examples, and is intended to include all changes recited in the claims and made within a meaning and a scope equivalent to the scope of the claims.

<Outline Configuration>

Hereinafter, a boiler 1 including a combustion apparatus 10 according to an embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 is a diagram schematically showing a configuration of the boiler 1 including the combustion apparatus 10 according to the embodiment of the present invention.

The boiler 1 includes a boiler body 2 configured to combust fuel to generate steam, an air blower 3 configured to send air into the boiler body 2 through an air supply path 30, a gas flue 4 configured to guide, e.g., exhaust gas out of the boiler body 2, and a fuel supply line (a fuel supply path) 5 configured to supply fuel to the boiler body 2. Note that an example where fuel is gas will be described, but fuel is not limited to gaseous body such as gas and may be a liquid body such as oil.

The combustion apparatus 10 includes a control unit 6, a flame detector 7 (a flame detection section), a pilot burner (a burner) 8, an ignition section 9, and a main burner 20. The main burner 20 is provided at a connection portion between the boiler body 2 and the air supply path 30, and combustion air is supplied to the main burner 20 from the air blower 3 through the air supply path 30. The pilot burner 8 is provided to face the inside of the air supply path 30.

The fuel supply line 5 is connected to the air supply path 30 and the pilot burner 8. Fuel supplied from the fuel supply line 5 to the air supply path 30 is mixed with air sent from the air blower 3, and the resultant is supplied to the main burner 20 in the boiler body 2. Fuel supplied to the pilot burner 8 is ejected from the pilot burner 8, and is mixed with air supplied from an upstream side of the air supply path 30. On-off valves (electromagnetic valves) 11, 12 for opening/closing a flow path and a fuel supply amount adjustment valve 13 are provided on the fuel supply line 5. The fuel supply amount adjustment valve 13 functions as a pressure adjustment valve capable of adjusting the flow rate of fuel supplied to the boiler body 2, and also has a blocking function. The fuel supply amount adjustment valve 13 is a motor valve which is provided downstream of the on-off valves 11, 12 and of which degree of opening is adjusted by the control unit 6. Note that the fuel supply amount adjustment valve 13 is not limited to the motor valve as long as the fuel supply amount adjustment valve 13 adjusts the fuel flow rate, and for example, may be an air control valve.

The ignition section 9 is an ignition apparatus (an igniter) configured to generate spark for igniting the pilot burner 8, and is provided on the air supply path 30. The pilot burner 8 is ignited by the spark generated from the ignition section 9 to generate flame. Using such flame, the main burner 20 is ignited to combust fuel in the boiler body 2.

The control unit 6 is implemented by a computer including a memory, a timer, and an arithmetic processing unit. The control unit 6 adjusts the flow rate of supplied fuel based on the flow rate of combustion air supplied to the boiler body 2 according to a combustion stage. That is, as the flow rate of combustion air increases, the control unit 6 increases the degree of opening of the fuel supply amount adjustment valve 13 to increase the flow rate of fuel. On the other hand, as the flow rate of combustion air decreases, the control unit 6 decreases the degree of opening of the fuel supply amount adjustment valve 13 to decrease the flow rate of fuel. The control unit 6 further includes a flame determination section (a flame determination function).

The flame determination section is a section configured to determine whether or not the flame is generated at least in the pilot burner 8, and determines generation of the flame based on a detection result of the flame detector 7 configured to detect the presence or absence of the flame of the pilot burner 8. The flame detector 7 is an optical detection section such as an ultraviolet phototube, a cadmium sulfide cell, or a lead sulfide cell, and detects the flame as light (including visible light and invisible light). As the flame detector 7, an ultraviolet detector configured to detect the presence or absence of the flame based on ultraviolet light, such as an ultraviolet phototube, is preferably used. However, the flame detector 7 is not limited to above, and may be a detector configured to detect visible light or infrared light. Note that the ultraviolet detector of the detectors is preferably used because the ultraviolet detector can be used without the ultraviolet detector being directly put in flame, is less likely to cause a problem on contamination due to adherence of soot or the like, exhibits excellent durability, is less likely to react with red heat of a furnace wall as compared to the detector configured to detect visible light or infrared light, and has a high blue flame detection accuracy.

The control unit 6 determines, based on a determination result of the flame determination section, whether or not fuel is to be supplied to the main burner 20. That is, the control unit 6 monitors the presence or absence of the flame by the flame determination section. For example, when it is, upon ignition, determined that the flame of the pilot burner 8 is generated, the control unit 6 starts a fuel supply to the main burner 20 to start combustion by the combustion apparatus 10. Thus, the flame determination section needs to prevent erroneous detection of, e.g., the spark generated by the ignition section 9 as the flame upon ignition and prevent the start of a fuel supply even though the flame of the pilot burner 8 is not generated.

<Operation>

Operation of the combustion apparatus 10 according to the present embodiment will be described with reference to FIG. 2. FIG. 2 is a time chart showing operation of the combustion apparatus, and shows a change in an ON/OFF state of the igniter as the ignition section 9 and an actuation (sampling) state of the flame detector 7. The flame detector 7 performs sampling in a constant actuation cycle. In a case where the flame detector 7 is an ultraviolet phototube, a drive voltage is applied in a constant cycle (e.g., a cycle of 5 msec) to perform ultraviolet detection. The flame determination section determines the presence or absence of the flame based on the detection result of the flame detector 7 in a determination period (e.g., 500 msec). Specifically, when the number of times of detection as the flame being present in sampling in the determination period (e.g., 500 msec) is equal to or greater than a predetermined number of times (a predetermined condition is satisfied), the flame detector 7 outputs information from which it can be determined that the flame is generated (ignited) to the flame determination section of the control unit 6. In a case where the determination period is 500 msec and sampling is performed in every 5 msec, the number of times of sampling is 100. The above-described information is obtained in such a manner that a flame current value is output from the total number of times of detection as the flame being present. When the flame current value exceeds a current value at an ignition determination level, the flame determination section determines that the flame is generated (ignited). On the other hand, when the flame current value is equal to or less than the current value at the ignition determination level, it is not determined that the flame is generated (ignited). Considering such an ignition determination flow by the flame detector 7, the ignition section (the igniter) 9 is provided with an ON/OFF timer (not shown) on a primary side such that the spark is generated in a particular period of the determination period (the igniter ON) and no spark is generated in the remaining period of the determination period (the igniter OFF), and adjusts the number of times of detection as the flame being present within the determination period by changing the ratio (a DT ratio: the particular period/the determination period) of the particular period to the determination period. With this configuration, the ignition section 9 ignites the burner without the predetermined condition for determining that the flame is generated being satisfied. One example of experiment results collected for each ratio of the particular period to the determination period is shown in FIG. 3.

FIG. 3 shows, as results, the number of times of determination as the flame being present upon pre-ignition and pilot burner ignition performance (the number of times of successful ignition) when the particular period (an igniter ON period) and the remaining period (an igniter OFF period)) are changed to a DT ratio of 0.5 to 0.01 in a case where the determination period is 500 msec.

Upon pre-ignition, no flame is generated by the pilot burner 8, and only the spark is generated. Thus, the number of times of determination as the flame being present upon pre-ignition indicates the number of times of erroneous detection determined as the flame being present due to the spark upon pre-ignition. At a DT ratio of 0.5 (a particular period of 250 msec), all of ten determinations are made as the flame being present. At a DT ratio of 0.3 (a particular period of 150 msec), two of ten determinations are made as the flame being present. At a DT ratio of 0.2 (a particular period of 100 msec) or lower, none of ten determinations are made as the flame being present. This means, at a DT ratio of 0.2 or lower, equal to or lower than the current value at the ignition determination level when the spark flies.

Regarding the pilot burner ignition performance (the number of times of successful ignition), all of ten ignitions are successful at a DT ratio of 0.5 to 0.1. In some cases, ignition is not successful at a DT ratio of 0.05 or lower, four of ten ignitions being successful at a DT ratio of 0.05, two of ten ignitions being successful at a DT ratio of 0.02, and one of ten ignitions being successful at a DT ratio of 0.01. Even at such a level that there is no erroneous detection, the DT ratio needs to be adjusted to such a range that the original purpose of the spark for igniting the pilot burner can be accomplished.

As described above, in a case where the determination period is 500 msec and sampling regarding the presence or absence of the flame is performed in every 5 msec, the particular period for which the burner is ignited without the predetermined condition for determining that the flame is generated being satisfied is those at a DT ratio of 0.2 and a DT ratio of 0.1 in FIG. 3. In the present embodiment, the DT ratio is set within a range of equal to or higher than 0.1 and lower than 0.3 so that a combustion apparatus capable of preventing erroneous detection of the spark as the flame while reliably igniting the burner by the spark can be obtained.

One example of operation of the boiler 1 according to the present embodiment will be described. At the start of combustion, the control unit 6 starts the air blower 3 to supply air to the air supply path 30. Thereafter, the control unit 6 outputs a start signal to the ignition section (the igniter) 9 to start the ignition section 9, thereby generating the spark. After the spark has been generated, the control unit 6 starts a fuel supply to the pilot burner 8 to ignite the pilot burner 8 by the spark from the ignition section 9. Then, the control unit 6 starts a fuel supply to the main burner 20 in the boiler body 2, thereby igniting the main burner 20 by the flame generated from the ignited pilot burner 8 to combust a supplied gas mixture. Meanwhile, the flame detector 7 detects the presence or absence of the flame. At this point, the ignition section 9 generates the spark across the particular period set as described above, and generates no spark in the remaining period. In this manner, the flame determination section (the control unit 6) does not make determination as the flame being present while the pilot burner 8 is reliably ignited. When the flame is generated by ignition of the pilot burner 8, the flame determination section makes determination as the flame being present, and a fuel supply to the main burner 20 is started. As described above, erroneous detection as the flame being present due to the spark can be prevented, and the start of a fuel supply to the main burner 20 regardless of the absence of the flame of the pilot burner 8 can be prevented.

The present invention is not limited to the above-described embodiment, and various modifications and applications can be made. Hereinafter, e.g., variations of the above-described embodiment applicable to the present invention will be described.

In the above-described embodiment, the example where the particular period is switched to the remaining period once in the determination period in the order of ON and OFF has been described (e.g., in the case of a DT ratio of 0.2, an ON time of 100 msec to an OFF time of 400 msec). However, the present invention is not limited to such an example, and switching can be made in the order of OFF and ON during the determination period. For example, in the case of a DT ratio of 0.2, switching may be made in the order of an OFF time of 400 msec and an ON time of 100 msec. Alternatively, switching may be made twice or more such that the total ON time and the total OFF time are the same as each other. For example, in the case of a DT ratio of 0.2, switching may be, without changing a total ON time of 100 msec, made twice in the order of an ON time of 50 msec, an OFF time of 400 msec, and an ON time of 50 msec. Switching may be, without changing a total OFF time of 400 msec, made twice in the order of an OFF time of 200 msec, an ON time of 100 msec, and an OFF time of 200 msec. Switching may be made three times in the order of an ON time of 50 msec, an OFF time of 200 msec, an ON time of 50 msec, and an OFF time of 200 msec during the determination period. Note that as long as the total ON time and the total OFF time are the same as each other in each determination period, time allocation of the ON time and the OFF time and the number of times of switching are not limited to constant time allocation and a constant number of times among the determination periods, and may be different among the determination periods (an irregular cycle). For example, switching may be made in irregular cycles in each determination period such that switching is made twice in the order of an ON time of 30 msec, an OFF time of 400 msec, and an ON time of 70 msec in a certain determination period and switching is made three times in the order of an ON time of 50 msec, an OFF time of 200 msec, an ON time of 50 msec, and an OFF time of 200 msec in another determination period.

In the above-described embodiment, the example where the flame detector 7 outputs the flame current value from the total number of times of detection as the flame being present in the determination period and the flame determination section determines the presence or absence of the generated flame (ignition) based on whether or not the flame current value exceeds the current value at the ignition determination level has been described. However, the present invention is not limited to such an example, and the number of times of detection as the flame being present in sampling can be also used as the information from which it can be determined that the flame is generated (ignited). In this case, when the number of times of detection as the flame being present is equal to or greater than a predetermined number of times, it is determined that the flame is generated (ignited). On the other hand, when the number of times of detection as the flame being present is equal to or less than the predetermined number of times, it is not determined that the flame is generated (ignited).

Note that the present invention is for preventing erroneous operation due to erroneous detection of the spark as the flame in a case where no flame is present, and the following advantageous effects can be also obtained. In a case where the flame detector 7 detects the flame at such a stage that the flame is not supposed to be present, the flame is generated in a region in the vicinity of the pilot burner 8. Thus, e.g., fuel leakage, remaining fuel, or an abnormality in the timer configured to turn on/off the igniter can be detected.

The embodiment disclosed herein has been set forth as an example on all points, and shall not be interpreted in a limited manner. The scope of the present invention is not recited by the description above, but is recited by the claims. The present invention is intended to include all changes made within the meaning and the scope equivalent to the scope of the claims. 

What is claimed is:
 1. A combustion apparatus comprising: a burner configured to generate flame; an ignition section configured to generate spark for igniting the burner; a flame detection section configured to detect a presence or absence of the flame of the burner; and a flame determination section configured to determine, based on a detection result of the flame detection section in a preset determination period, whether or not the flame is generated at the burner, wherein when a predetermined condition is satisfied based on the detection result of the flame detection section in the determination period, the flame determination section determines that the flame is generated, and the ignition section generates the spark across a particular period, in which the predetermined condition is not satisfied, of the determination period, and does not generate the spark in a remaining period of the determination period.
 2. The combustion apparatus according to claim 1, wherein the flame detection section detects the presence or absence of the flame based on ultraviolet light.
 3. The combustion apparatus according to claim 1, wherein the particular period is a period in which the burner is ignited without the predetermined condition being satisfied.
 4. The combustion apparatus according to claim 1, wherein the predetermined condition is satisfied according to the number of times of detection as the flame being present by the flame detection section in the determination period. 